Abstract

We present the results of a combined experimental and theoretical investigation of sedimentation in a stratified fluid. The theory of sedimentation in a homogeneous ambient is extended to include the influence of a spatially varying particle settling speed. The results of an experimental investigation of latex particles settling in a stably stratified salt water solution are reported. Density variations in the suspending fluid reduce the particle settling speed which increases particle concentrations, thus enhancing the effects of hindered settling. A criterion is developed for the convective instability of an initially uniform suspension settling in a stably stratified ambient. If, as depth increases, the magnitude of the ambient density gradient decreases sufficiently rapidly, an initially uniform particle concentration will give rise to a statically unstable density profile. Experimental observations provide qualitative verification of this new stability criterion.

The authors thank Tom Peacock for his selfless help in setting up the experiments and Jeff Parsons for a number of valuable discussions. F.B. was supported in part by a PSG-B fellowship from NSERC and by the Schlumberger Foundation. J.B. gratefully acknowledges support from an NSF Career Grant No. CTS-0130465.